This section outlines the threats and opportunities which are created by the interaction of man with waterways and wetlands. Throughout history, the maintenance of fresh water supplies has been essential for the survival of cultures, for domestic life, agriculture and industry. Waterways for transport, water supply and defence have determined the pattern of urban settlement. Some of man’s actions have been of benefit, with industry creating such features as the Norfolk Broads, the canal system, and the many gravel pits and reservoirs which have become valuable wildlife habitats. However, the 20th Century was characterised by pollution, abstraction, draining of wetlands and engineering of rivers. There are many initiatives to restore habitats, reduce pollution and return to more natural methods of river management, but serious problems remain:
- Pollution from sewage effluent, which requires huge investment in improved treatment systems. Pollution from agricultural waste can only be lessened by reducing inputs and establishing buffer zones.
- Ever increasing demands for water for industrial and domestic use, requiring increased abstraction, resulting in lowering of river levels and water tables.
- Increasing recreational pressures from watersports, angling and other outdoor activities.
- Climate change, which appears to be resulting in a reduction of annual rainfall in the UK; a trend which is predicted to continue.
Springs, ponds and lakes
Springs are insulated against the worst effects of pollution, although nitrate ions from fertilisers can percolate through the rock strata. Springs are more often threatened by ground water extraction which lowers the water table and cuts them off from their sources of supply.
Ponds and lakes, whether natural or artificial, may be threatened by pollution. This is caused more often by excess nutrients entering the water than by directly toxic substances. Domestic wastes and certain industrial by- products are major sources of nutrients, as are fertilisers, silage and slurry effluent. Inputs of phosphate from sewage on rivers in the Norfolk Broads is estimated to have increased tenfold since the beginning of the 20th Century. The ecosystem of many Broads effectively collapsed due to eutrophication, with algae dominating in turbid water. Since the early 1980s, phosphate has been removed at eight sewage works which discharge into Broadland rivers. Restoration measures on some Broads have included the injection of iron to bind the phosphorus, the pumping of mud, and removal of fish to allow water flea populations to increase, which in turn reduce algal blooms by grazing.
Problems of excess eutrophication are often interlocked with those of ecological succession. Many of the Broads, for example, have filled in over the years with fen detritus. Those that were too deep to drain in the last century are now very near the threshold at which rooted plants can spread across the surface. When this happens the Broad, being of nearly even depth throughout, quickly silts up and develops into fen. The same progression affects other small water bodies, such as farm and village ponds. Without maintenance these ponds slowly fill in and turn to scrub or grassland.
Questions of access and use create major problems on open water bodies of all types. Where one purpose is of overriding concern it may be easy to decide an appropriate policy for the number of people allowed onto a site, and the means by which they are allowed to use it. Conflicts may arise where several incompatible users have interest in a site, but zoning in time or place may allow satisfactory multiple use. On many sites, for example, wildfowlers and fishermen work in co-operation with conservationists, and can often assist in management work with finance, labour and expertise. Zoning works best on large water bodies. Where there are a number of smaller ponds it is best to restrict each to one or two compatible activities.
Streams and rivers
Over the centuries man has greatly altered many rivers and their floodplains. Lowland rivers have been straightened, widened and deepened to prevent flooding and increase water flow, destroying much of the natural habitat of the river. Floodplains have been drained for agriculture and development. This causes an actual loss in valuable wetland habitat, as well as the loss of the buffering and absorptive effect of wetlands. Heavy rains are rapidly drained off into rivers, causing high flows which then need controlling, and with less water being absorbed and reaching the vital underground aquifers. Rapid run-off from drains and hard surfaces washing into rivers also results in siltation, pollution and other problems. During dry spells of weather, there is no slow seepage from wetlands to help maintain river flows, and water levels drop dramatically.
In general, an alteration to one part of a river system has effects elsewhere that usually result in the need for further interference. However since the 1980s, the importance of conserving natural habitat has been realised, with much more emphasis from the Environment Agency and other organisations on using ‘soft’ engineering techniques for river revetment, and the protection of natural river features such as meanders and riffles. With so many streams, rivers and their flood plains altered irreversibly for urban development, the protection of remaining natural habitat becomes even more important.
Pollution from industrial wastes, agriculture and sewage continues to be a problem. Although some rivers, notably the Mersey and parts of the Thames, are much cleaner than they were in the mid 20th Century, and in spite of a reduction in industrial pollution and the banning of some persistent chemicals, pollution is still a problem. The 1990 Rivers Survey by the National Rivers Authority reported a net deterioration in river quality over the previous decade, partly due to increased sewage effluent. Quality had deteriorated due to deoxygenation from bacterial breakdown of waste material, toxic effects of ammonia, some pesticide residues, and eutrophication. Surveys by English Nature and other conservation bodies have identified in particular an alarming increase in phosphate, mainly from domestic sewage effluent, but with a significant proportion from agricultural wastes. Phosphate favours fast growing plants, which outcompete more sensitive species. In slow flowing rivers, algae and blanket-weed dominate, suppressing other plants and causing deoxygenation of the water.
In upland rivers, a small increase in phosphate can greatly alter the plant community. Measures need to be taken at several levels. Inputs from detergents and other cleaning agents should be drastically reduced by only allowing phosphate-free products. Phosphate removal is needed at sewage treatment works to remove the phosphate which enters the system from the food we eat. Input of phosphates from agricultural fertilisers needs reducing, together with the greater use of buffer strips and water fringe habitats to absorb phosphates before they enter ditches and streams.
Changes are being made to try and reduce many types of pollution, and to manage rivers in a more natural way. Agricultural schemes including Set-Aside, Environmentally Sensitive Areas (ESAs), Nitrate Sensitive Areas and others should benefit water quality and riverbank habitats. Environmental Assessment legislation requires all works with the potential to have significant effect on the environment to be subject to formal asessment. This covers many types of river management and maintenance work. The formation of the National Rivers Authority in England, now part of the Environment Agency, is resulting in river management being planned in a more holistic manner, rather than on a site by site basis. Wildlife and conservation issues are an important part of their agenda.
While improvements are being made on some fronts, weather patterns and climate change have conspired against us. The 1990s were characterised by severe droughts in much of the country, with many rivers down to less than half their normal flow. The lack of rain has lowered the water table, with many aquifers in the North East, North West and East Anglia at an all time low. Meantime, domestic and industrial demand for water continues to rise. In the autumn of 1995, many water companies were faced with near empty reservoirs, and successfully applied for drought orders to allow the emergency abstraction of water from feeder rivers. The expected winter rain of 1995/96 never came, and as water companies abstracted the water, river levels dropped further. In August 1996, English Nature reported that 89 sites of natural and special scientific interest has been damaged by excessive abstraction.
With the long-range outlook a continuing warming and reduction of rain over a long cycle of years, reduction in demand, conservation of supplies and the stopping of leakage from supply pipes is essential if rivers are to recover. Borehole extraction from aquifers for agricultural use has been reduced or stopped in many areas, together with abstraction from rivers and streams. It is likely that larger farms will increasingly invest in building their own reservoirs to ensure continuity of supply.
Leats, ditches and canals
Traditional labour-intensive cutting and clearing of ditches and canals has given way to quicker, cheaper and more thorough methods which can severely disrupt the aquatic ecosystem. Dredging is easily mechanised and can be done on a vast scale. Small drainage ditches, both natural and artificial, may be piped in to increase land-use efficiency. Piping in destroys their value as ‘linear nature reserves’ which are so vital for the survival of wildlife, especially in the hedgeless agricultural landscapes of areas such as East Anglia and Lincolnshire. Ditches are also important for the spread of aquatic plants, many of which propagate from broken pieces of stem or root which are carried along in the water. This is why plants soon recolonise dredged areas if ‘sanctuaries’ are left between the cleaned-out sections. In recent years, authorities responsible for watercourse management have shown increasing interest in methods of management which are more compatible with wildlife, and which also create a more natural, stable way of managing water resources. These include partial dredging, rotational cutting of bankside vegetation, and retention of meanders, ox-bow lakes and other natural river features. For further information, see RSPB, NRA and RSNC (1994).
Artificial channels can also be harmed by neglect. As canals decay their wildlife value may improve up to a point, but when completely choked in reedswamp or silted up and dried out they again decline in interest and diversity. Wetlands nature reserves, especially in East Anglia, often contain elaborate drainage and access channels dating from the last century or earlier, sometimes equipped with pumps and sluices to control levels and prevent their drying out. Usually these areas have suffered a generation or more of disuse and dereliction by the time they receive reserve status, so much renovation work is required before their survival can be guaranteed. Once restored, they offer an unparalleled opportunity for the maintenance of a mosaic of habitats and for controlled experiments in ecosystem development.
Swamps and marshes
Swamps and marshes develop on fertile silt and peat soils which are attractive for agricultural reclamation. Drainage has fragmented lowland swamps and marshes, such as the great arc of marshland around the Wash, north of the Fenland proper, which been converted to rich pastures and horticultural land. Housing and industrial estates often drain wetlands piecemeal or fill them with spoil. Swampy fringes of open water suffer from waterway maintenance programmes, especially dredging.
Conservation of swamps and marshes must be carried out not only to save them from these threats but also to avoid similar damage in the pursuit of management. Footpaths and trackways often disrupt the hydrological balance of wetlands even if they don’t actually drain them. Pond, lake and channel clearance to protect open water habitats or provide access and recreation should be planned carefully to minimise destruction of fringe vegetation. Development of new waterways can destroy existing swamps and marshes but may also ensure their continuation by providing suitably graded banks and shallows. The Great Linford wildfowl reserve in Buckinghamshire is made up mainly of rather deep lakes created through gravel extraction operations, but fringes of reedswamp and marsh have been developed through extensive shoreline plantings, a bulldozed ‘scrape’ and the fencing of adjacent wetlands against grazing by cattle.
Wet grasslands
The most interesting lowland wet grasslands occur along the larger river valleys, but here they have been decimated by drainage, flooding, clearance or dredging. Even the Ouse Washes have at various times been suggested for ploughing or flooding for a reservoir. Water meadows, unlike some grasslands, need unbroken traditional management to maintain their historical and wildlife interest. Once their sluices and aqueducts cease to function they revert to drier conditions. A few areas have been maintained throughout this century, forming precious reserves of wet grassland flora and fauna. Hopefully the tide of neglect and destruction is now turning, and in recent years several areas have been restored or created. These include water meadows on the River Avon at Britford, south of Salisbury, and on the River Windrush, at Sherborne in Gloucestershire.
The characteristic plants of flood meadows are dependent upon continuous traditional management, since species such as the fritillary persist only where there is winter flooding, quick spring drainage and summer mowing which keeps down ranker plants.
Sand and gravel extraction eliminates flood meadows and other wetlands. Extraction advanced so rapidly during the latter part of the 20th Century that many important sites have vanished. Extraction can produce new areas of open water which can, with time, become valuable habitats. Some pits have been partially refilled with other material and restored as wetlands. This does not, however, compensate for the loss of the original wet grassland habitat which can never be recreated.
Mires
The threat to mires throughout the world is so severe that enormous effort has been put into their protection by many conservation organisations. Upland mires, though less accessible that those in the lowlands, are in some ways the most vulnerable. Raised and blanket bogs, particularly, break down and ‘waste’ once the surface vegetation is killed. This can be clearly seen on Kinder Scout and elsewhere in the Derbyshire Peaks where fires, trampling and air pollution have led to widespread dissection of the blanket bog into blocks of deep peat cut by a maze of treacherous drainage channels. Improvements are slowly being made by the provision of resistant path surfaces, liming and reseeding, and the reduction of grazing.
Grasses, bracken and scrub species are adapted to take advantage of fires and are able to regrow or seed very quickly into burned areas. The release of nutrients from burned vegetation further favours these plants at the expense of Sphagnum. Heavy burns or fires in peat which is already dry ignite the peat itself, which smoulders indefinitely and is then easily eroded by wind and rain. Trampling pushes bog plants below water, killing them and leaving pools in their place. Even one or two people struggling across a raised bog may make a lasting impression, one reason why study or management of such sites is difficult. Sulphur dioxide from burning coal and car exhaust may descend as ‘acid rain’, upsetting the meagre nutrient supply of raised bogs especially. The shift in the 18th and 19th Centuries from Sphagnum bog to cottongrass (Eriophorum) moor in the Pennines is thought to have been caused partly by industrialisation in Lancashire and the resulting air pollution carried eastward by the prevailing winds.
Lowland bogs and fens are less susceptible to fires, trampling and pollution although damage is possible, especially where public pressure and vandalism become intense. Their vegetation balance may be upset by a change in the water nutrient status, although the effect is often confined to a narrow strip along ditches which bring eutrophic water into the mire. But if the ditches overflow, acid-loving plants across the bog surface are destroyed. Fens and some lowland bogs are susceptible to natural scrub invasion which may require combating if the mire is to survive. Scrub clearance is a major aspect of vegetation management on many lowland sites and is detailed in a later chapter.
Drainage and peat cutting have decimated many mires, especially in the lowlands where today only a few relics remain. These are often extremely important as ‘islands’ of high wildlife value in a sea of relatively impoverished agricultural land. Peat was, until recently, an important fuel throughout rural Britain wherever firewood was scarce, as it still is in isolated parts of Scotland and Ireland. In most cases the effects of traditional peat cutting are limited and transient. Some lowland Welsh, Scottish and Irish bogs have been reduced in size over the years, but because cutting must cease when the water table is reached, unless pumps are used, traditional methods tend to take a thin layer off an area and then abandon it or turn it over to grazing while the vegetation recovers and another area is scalped in turn. This often produces a valuable diversity. Slightly raised mires with alkaline ground water, for example, may develop a series of habitats from alkaline pools and water level peat to moderately acid peat at the original mire level to highly leached and acid ridges or baulks, well above ground water, where the top vegetation is piled after being cut away. Even bogs unaffected by alkaline ground water may develop slight variations in acidity and waterlogging due to cutting, which allows a greater variety of plants to flourish than would otherwise exist.
Some of these worked-over mires today form nature reserves of great interest. Often the areas most desirable to preserve are the ‘poor ’s fens’, so called because they were set aside for the use of paupers and pensioners. While many privately-owned mires were drained for pasture, ploughland or plantation, the poor ’s fens often remained unimproved and in use up to the l930s or later. Unfortunately, ownership of these areas is now often obscured by the unofficial demise of the original controlling charities. When nobody is left to exercise cutting rights, these fens quickly revert to scrubland.
The demand for peat has vastly increased in recent years, mainly for horticultural purposes but also for use in such diverse fields as distilling, animal husbandry, medicinal baths and the production of biostimulants and peat wax. In Ireland peat is now used to fuel large-scale electrical power stations and peat ‘mining’ is highly organised. Shapwick Heath in Somerset is the major English source of high-grade sedge peat. Here the largest companies use machines each of which replaces fifteen men cutting by hand. The machines must be kept in continuous use, if possible, which requires hundreds of acres to be kept open for cutting at any one time. It may take five to seven years to cut the top layer off an entire field. Cutting then begins at a new and lower level, continuing intermittently until subsoil clay is reached or until it is no longer economic to pump the fields dry.
The Somerset peat moors are designated by the IUCN as being of international scientific importance, both for their present-day flora and for the plant remains and archaeological evidence which they preserve. Mining, which will eventually include most of Shapwick Heath NNR, destroys this. Mined areas can be left to regenerate naturally to woodland or they may be reclaimed for grazing. New peat, however, cannot be formed since climatic conditions are now unfavourable. It is planned to turn some of the exhausted Somerset peat fields into lakes for flood control and recreation, but it seems unlikely that these new features will develop anything to compare with the biological richness of the old.
